Design of nondispersion optical feedback system using diffraction grating for semiconductor laser multiple longitudinal modes control

The external optical feedback system with a diffraction grating and mirrors is designed as a light source system in wavelength division multiplexing transmission. This system can select not only oscillation center wavelength but also spectral range in semiconductor lasers by using an identical grating twice. Experimental results demonstrate selected oscillations of single and double longitudinal modes in a multimode semiconductor laser.     

Scanning the laser gain spectrum using distributed feedback and hydrostatic pressure

High-pressure measurements on distributed-feedback GaxIn1-xASyP1-y lasers allow the gain spectrum to be scanned, providing a powerful tool for the study of the intrinsic properties of the laser, including the mechanisms responsible for the high-temperature sensitivity.     

Broad-stripe near-diffraction-limited mid-infrared laser with a second-order photonic-crystal distributed feedback grating

Electron-beam lithography was used to pattern a second-order photonic-crystal distributed feedback grating onto an antimonide type-II "W" laser emitting at /spl lambda//spl ap/3.7 /spl mu/m. For pulsed optical pumping, the output beam was essentially diffraction-limited up to a stripe width of 150 /spl mu/m, and remained no worse than eight times the diffraction limit for stripes as wide as 600 /spl mu/m. This represents a considerable improvement over all previous mid-infrared semiconductor lasers with such broad stripes.     

Single-mode operation characteristics of a self-injection seededFabry-Perot laser diode with distributed feedback from a fiber grating

We study the operational characteristics of a self-injection seeded laser diode in an external cavity consisting of a fiber Bragg grating. The distributed feedback (DFB) of light in the grating provides an additional tolerance of frequency detuning in mode selection. The spectral characteristics at different operating frequencies and feedback rates have been investigated. Wavelength tuning has also been realized by applying compressive and tensile strain to the grating and a tuning range of 11.6 nm has been obtained     

紧凑型光栅外腔可调谐半导体激光器

研制了一台结构紧凑的窄线宽、可调谐半导体激光器.采用光栅外腔Littrow结构,将光栅和平面反射镜置于同一个旋转平台上,并使光栅衍射平面和平面镜反射平面的交线与平台旋转轴重合,通过旋转平台实现光栅外腔选取单纵模、压窄线宽和波长调谐,并保证输出光的方位不发生改变,同时用棱镜将输出光斑压缩成为类方形.该激光器的尺寸为110 mm×80 mm×35 mm,中心输出波长为653 nm,谱宽0.07 nm,调谐范围4.6 nm,可连续稳定运转4小时以上.     

Zero-power gain measurements in a CW HF laser using a pulsed-probe laser

Zero-power gain measurements in a supersonic diffusion-type CW HF laser have been made using a pulsed HF probe laser. A peak zero-power gain of 10 percent/cm was measured on aP_{2}(3)vibrational-rotational transition and 7 percent/cm on aP_{1}(6)transition for flow rates corresponding to 1.8 kW of closed-cavity power. The variation of zero-power gain with rotational quantum numberJfits a simple rotational equilibrium model indicating increasing rotational temperatures with increasing distancexfrom the nozzle exit plane. The model also indicates a total inversion forx leq 0.2in for theP_{2}(J)transitions and a partial inversion further downstream.     

Degradation analysis in asymmetric sampled grating distributed feedback laser diodes

This paper presents the experimental observation of the degradation in asymmetric sampled grating DFB lasers by the accelerated life tests. Two degradation phenomena related to the electrical characteristics of LDs are observed during the tests. The first degradation phenomenon by increasing the reverse current is considered as a formation of leakage current path enough to prevent lasing operation in lateral blocking layer near active region of lasers. The second degradation phenomenon by decreasing the forward current is considered as activation of non-radiative Auger recombination process by thermal energy. It is also experimentally observed that the second degradation phenomenon is recovered after remained in room temperature with no electrical stress. Therefore, the criteria for LD reliability can be determined by observing the degradation of the reverse current–voltage characteristics.     

Wideband gain flattened erbium fibre amplifier using a photosensitive fibre blazed grating

An erbium fibre amplifier with a highly flattened gain spectrum is demonstrated for the first time using an all fibre photosensitive Bragg grating. An ASE spectrum flattened to within +or-0.5 dB over a bandwidth of 35 nm in the 1550 nm window is achieved with a 3 mm long radiation coupling Bragg fibre grating.<>     

Electrical control of the distributed feedback organic semiconductor laser based on holographic polymer dispersed liquid crystal grating

In this paper, we demonstrate the electrical control of the distributed feedback (DFB) organic semiconductor laser based on a holographic polymer dispersed liquid crystal (HPDLC) grating for the first time. The grating is fabricated on the top of the organic semiconductor film to act as an external feedback structure. Experimental results show that the lasing intensity can be decreased by increasing the external electric field, and the lasing wavelength exhibits a slight blue-shift of 1.4 nm during the modulation process, indicating a good stability. The modulated performances are attributed to the decreases in the refractive index modulation and average refractive index of the HPDLC grating respectively as a result of the field-induced liquid crystal reorientation. This study provides some new ideas for the improvement of DFB organic semiconductor laser to enable envisioned applications in laser displays and integrated photonic circuits.     

Approximate analysis of gain saturation of a distributed feedback laser with end reflectors

An approximate method for the analysis of distributed feedback lasers is presented. An expression for the small-signal gain coefficient αoNas a function of the output power PNoutnormalized to the saturation power Ps, coupling coefficientk, complex reflectivity of the end reflectorsR, and length of the laserLis obtained. The results are found to be in good agreement with published computer solutions.     

Identification of linear time-invariant system using feedback gain

Feedback property and exponential curve fitting are used to identify the parameters of transfer function. It is assumed that all state variables are inaccessible for measurement.     

Fiber laser polarization tuning using a Bragg grating in a Hi-Bifiber

Single- and dual-wavelength tunable lasing (around 1552 nm) has been obtained in an Er-doped low-Bi fiber laser with a Bragg grating mirror in a Hi-Bi fiber. Equal output powers for both laser lines and spectral spacing of up to 0.26 mm, larger than the original spacing between the resonance peaks of the grating (0.2 nm), can be easily achieved by employing a polarization controller inside of the laser cavity     

Narrow line semiconductor laser using fibre grating

A narrow linewidth, low chirp, wavelength selectable, packaged alternative to current DFB structures has been developed which employs a fibre reflection grating incorporated in the fibre pigtail. The wavelength of the packaged device can be determined by the appropriate choice of fibre grating coupled to the antireflection coated facet of a 1.55 mu m BH laser. Linewidths of less than 50 kHz, sidemode suppression of more than 30 dB and chirp when modulated at 1.2 Gbit/s of <0.5 MHz have been demonstrated.<>     

Characteristics of a semiconductor laser coupled with a fiber Bragg grating with arbitrary amount of feedback

Stationary characteristics (such as laser frequency at threshold, light-intensity curve, etc.) and relative intensity noise of laser diodes coupled with an external Bragg reflector are studied for arbitrary amount of optical feedback. We put the stress on the interplay between external and internal cavities when the feedback strength is increased. For strong feedback, new stationary solutions that do not exist in the case of conventional feedback appear, while the ellipse, which usually contains the modes and so-called antimodes, collapse in the plane frequency-gain. Finally, analytical expressions are compared with numerical results obtained through a new approach that uses Green functions.     

Dynamic output feedback sliding-mode control using pole placement and linear functional observers

This paper presents a methodological approach to design dynamic output feedback sliding-mode control for a class of uncertain dynamical systems. The control action consists of the equivalent control and robust control components. The design of the equivalent control and the sliding function are based on the pole-placement technique. Linear functional observers are developed to implement the sliding function and the equivalent control. Stability of the resulting system under the proposed control scheme is guaranteed. A numerical example is given to demonstrate its efficacy.     

Subnanosecond tunable laser using a single electroabsorption tuning super structure grating

A new tunable laser structure using a single electroabsorption (EA) tuning super structure grating section for fast wavelength switching operation, has been realized. The tuning mechanism of this absorption change distributed Bragg reflector (DBR) laser is based on a localized absorption variation induced in a multielectrode EA-SSG section. These devices exhibit a 2.5-nm tuning range with three modes and a switching time, between two successive wavelength channels, shorter than 250 ps. The output power variation under tuning is lower than 1.2 dB.     

一类混沌系统的动态输出反馈控制

为了对一类混沌系统实施控制,提出了利碍新的控制器来控制混沌系统。以往的混沌控制方法只针对个别特殊的混沌系统,而利用动态输出反馈的方法能控制一类混沌系统,这方面的工作以前也曾有过。利用李雅普诺夫稳定理论,结合线性矩阵不等式优化方法,分析了系统的稳定性。数值仿真也表明了所提出的控制策略的有效性。     

Far-infrared laser action using compound grating Fabry-Perot resonators

A water vapor laser has been operated with a subsidiary grating Fabry-Perot resonator replacing one end mirror. Double-wavelength operation was obtained. Single-wavelength operation was obtained with strong rejection of shorter wavelength radiation, a variable effective reflectivity of the end mirror, and control of polarization characteristics of the cavity, allowing linear or circular polarization.     

Dynamic gain and output power control in a gain-flattenederbium-doped fiber amplifier

We demonstrate an erbium-doped fiber amplifier (EDFA) that has a flat-gain spectrum over an 18-nm band and a constant per-channel output power regardless of the input powers and the number of channels. The gain flatness and the constant output are obtained by changing the laser diode pump power and the attenuation of the voltage-controlled attenuator (VCA) dynamically. The response times of pump control circuit and attenuator control circuit are 650 ns and 9 ms, respectively. The power excursion of surviving channel in an EDFA with fast control circuit is ~1% of that without fast control circuit when channels are added or dropped     

Coherent FSK transmitter using a negative feedback stabilised semiconductor laser

An electrical negative frequency feedback scheme is applied to a semiconductor laser to improve its direct frequency modulation performance in an FSK transmitter. An error signal caused by imperfect FM response is extracted through heterodyne discrimination detection with a stable master laser and fed back to the FM semiconductor laser.